The present invention relates to high voltage electrochemical double layer capacitors (EDLCs) and, more particularly, to a prototype design, manufacturing methods and materials to create electrodes for a high voltage EDLC, while maintaining high capacitance and low resistance thereof.
An electrochemical double layer capacitor (EDLC) is an energy storage device consisting of two electrodes arranged in such a manner that one acts as the cathode and the other the anode, creating a structure that can be modeled as two capacitors in series. The device is characterized by a high power density whose value can be dictated by the effective series resistance (ESR) of the device (i.e., the lower the ESR, the higher the power density). The capacitance of EDLCs can be large due to the effective surface of activated carbon used to fabricate an EDLC and the spacing between the electrode and the molecules of the electrolyte that form the double layers. The capacitance of an EDLC can be calculated using the formula C=kA/d, where k is a constant of proportionality, A is the effective surface area of the activated carbon, and d is the spacing between the electrode and the electrolyte molecules.
EDLC devices can be manufactured by encasing electrodes and separator material in a package which is wetted with electrolyte and sealed. The resulting device is a single cell EDLC device. These devices can be used in a wide variety of applications including but not limited to industrial power supplies, UPS (uninterrupted power supplies), electric vehicles, cell phones, and electronic appliances.
Known EDLCs operate with a nominal voltage rating of approximately 2.7 volts, a limitation imposed by virtue of the electrolyte. In some applications, more than a single EDLC cell is required to meet the needs of a particular application. For example, one or more EDLC devices can be coupled in series to provide a composite device that operates at a higher voltage. However, if the cells are not balanced as the number of cells in series increases premature failure of the composite device can occur. Additionally, the increase of the ESR of the cells in series can result in a decrease in power density.